Proportional throttle valve

ABSTRACT

The invention relates to a proportional throttle valve comprising a valve piston ( 2 ) which is displaceably guided in the longitudinal direction in a valve housing ( 3 ) having a fluid inlet ( 4 ) and a fluid outlet ( 5 ) and is pretensioned by an energy accumulator, in particular in the form of a pressure spring, against a stroke stop ( 6 ) defining the closure position. The invention is characterized in that a pressure limiting valve ( 7 ) is integrated in the proportional throttle valve ( 1 ), wherein said pressure limiting valve allows to influence the fluid pressure on the rear side ( 8 ) of the valve piston ( 2 ) in order to allow the piston to move away from the stroke stop ( 6 ) in opposition to the pretensioning force when a predefinable pressure is exceeded at the fluid inlet ( 4 ).

The invention relates to a proportional throttle valve comprising a valve piston which is movably guided in the longitudinal direction in a valve housing having a fluid inlet and a fluid outlet and which is pretensioned by an energy accumulator, in particular in the form of a compression spring, against a stroke stop defining the closed position.

Proportional throttle valves are often used when the level of the fluid flow passing through these valves is to be continuously changed as a function of a prevailing magnetic flow of a coil actuating the valve piston. With a view to a construction as a slide valve, the opening cross section is dependent on the piston position. If the coil is supplied with an electrical current, a magnetic force proportional to the magnetic flow is generated, as a result of which the valve piston can be moved into an open position. Here a spring located on the back side of the valve piston is generally tensioned; its spring force opposes the magnetic force. If an equilibrium is established between the magnetic force and the spring force, the valve piston remains in its position.

The proportional throttle valve is largely independent of the pressure level to be controlled because the valve piston is pressure-equalized by the pressure prevailing on the two end surfaces as well as in the pilot chamber.

Proportional throttle valves are used, for example, in lifting-lowering applications, such as in industrial trucks. In these applications, a 2/2 directional valve is typically used in the course of the lifting-lowering motion for lowering the load. At the same time, proportional throttle valves are used to control the volumetric flow. To protect the entire system of the two aforementioned valves, a pressure limiting valve is used in addition to limit the maximum pressure.

The known systems thus have a plurality of valves which require the corresponding installation space.

With respect to this initial situation, the object of the invention is to devise a proportional throttle valve that integrates in itself several functions with respect to the lifting-lowering motion.

This object is achieved by a proportional throttle valve having the features specified in claim 1 in its entirety.

In that, according to the characterizing part of claim 1, the proportional throttle valve integrates a pressure limiting valve, using which can facilitate influencing the fluid pressure on the back side of the valve piston for purposes of opening on the pertinent valve seat when a definable pressure is exceeded at the fluid inlet, a combination of the function of the proportional throttle valve with the pressure limiting valve is created which helps save components and installation space compared to the prior art.

Preferred embodiments will become apparent from the dependent claims.

The pressure limiting valve is preferably integrated into the valve piston for functional coupling of the control lines, the control lines causing at least the fluid pressure at the fluid inlet of the proportional throttle valve to act on a valve seat, especially made in the form of a cone seat of the pressure limiting valve. Here the fluid pressure from the fluid inlet is applied via a radially offset axial bore in the valve piston to the back side of the valve piston via an orifice bore and a bore running axially in the valve piston as well as via a radial bore which drains from the latter bore to a pilot chamber of the valve. Thus pressure equalization is effected. This fluid pressure also acts at the same time on the valve seat of the pressure limiting valve, and, if the pressure exceeds the value which has been set permanently on a valve spring of the pressure limiting valve, a control channel to the fluid outlet is cleared. The pilot volumetric flow being established at this point from the fluid inlet via the lateral axial bore in the valve piston, the back side of the valve piston as well as the orifice with the connected axial bore to the valve seat of the pressure limiting valve effects a pressure drop at the orifice. This reduced fluid pressure is signaled to the pilot chamber, from which a resulting force against the main spring of the valve piston results and moves the valve piston in the direction of an “open position” between the fluid inlet and the fluid outlet.

This mechanism of action is possible essentially both in the deenergized and also in the energized state of the proportional throttle valve so that a continuously available pressure limitation situation is integrated into the proportional throttle valve.

The invention is detailed below using the drawings. The single FIGURE shows schematically and not to scale a longitudinal section through a proportional throttle valve according to the invention.

The aforementioned FIGURE shows, in a longitudinal section, a proportional throttle valve 1 which is directly controlled in terms of its fundamental design. In a magnet system housing, there is a magnet system 14, wherein an armature 16 is actuatable by a DC coil 15. The magnet system 14 is designed as a pushing, path-controlled proportional magnet system, the armature 16 and an actuating element 17, which is dynamically connected to it, being moved down in the direction of a fluid inlet 4 in the energized state of the DC coil 15.

The actuating element 17 is dynamically connected to a valve piston 2 representing an orifice function. In the deenergized state of the DC coil 15, the armature 16, which is not detailed, the actuating element 17, and the valve piston 2 are moved by a spring 18 in the direction of a stroke stop 6. This corresponds to the closed state of the proportional throttle valve and the closed state between fluid inlet 4 and fluid outlet 5. The armature 16 is mounted inside in the pole tube.

The magnet system housing with a cylindrical guide 19 is designed to project into a valve housing 3 and is sealed for this purpose relative to the exterior. The cylindrical actuating element 17 likewise projects into the cylindrical guide 19 and has a detachable positive connection to a prolongation 20 of the valve piston 2, which prolongation guides the spring 18 on the mandrel side. The prolongation 20 undergoes transition through a cylindrical spacer 21 with a bottom 22 defining the stroke stop 6 into the valve piston 2 configured as an “orifice piston.” The stroke stop 6 accordingly separates the back side 8 of the valve piston 2 from its main control section 23.

The valve piston 2 has the main control section 23 for triggering the flow rate from the fluid inlet 4 to the fluid outlet 5. For this purpose, the main control section 23 has an inlet opening 24 and radial outlet openings 25. As a function of the positioning motion of the armature 16 of the magnet system 14, the outlet openings 25 can be caused to partially or completely line up with the fluid outlet 5 on the valve housing 3 when the valve piston 2 is moved in the direction of the fluid inlet 4.

In order to be able to superimpose a pressure limitation function on the volumetric flow control function of the proportional throttle valve 1, the main control section 23 of the valve piston 2 has an inner bore, which is concentric to its longitudinal axis 26 and into which a pressure limiting valve 7 is inserted. The pressure limiting valve 7 has a cylindrical housing 27 in which a valve cone 29 is placed on a valve seat 9 with pretensioning by means of a compression spring 28. The housing 27 of the pressure limiting valve 7 is permanently connected to the sleeve-shaped main control section 23 of the valve piston 2 and is guided to be able to move in the longitudinal direction with the latter. Within the framework of the fluid to be routed, the main control section 23 thus communicates with different control bores for triggering, especially relating to the fluid pressure on the back side 8 of the valve piston 2.

As a rule, a boundary pressure, which can be set via a compression spring 28 at the fluid inlet 4, causes an actuation of the valve piston 2 for purposes of a displacement motion of the valve piston 2 in the direction to the fluid inlet 4 and enables a volumetric flow to pass through the proportional throttle valve 1.

The pressure at the fluid inlet 4 itself is transferred via an axial bore 10, which is radially offset in the main control section 23 to the back side 8 into the spring space there, and the axial bore 10 in the region of the stroke stop 6 discharges from the valve piston 2. Out of the spring space, the pressure propagates via an orifice bore 11 in the prolongation via a bore 12, which is routed in this prolongation 20 and which is closed by the valve cone 29 of the pressure limiting valve 7. With a small axial distance from the valve cone, a radial bore 13 branches off from the bore 12 and leads into a pilot chamber, which is not detailed, as a result of which the main piston or valve piston 2 is pressure-equalized.

If at this point the pressure at the fluid inlet 4 exceeds a definable value, the valve cone 29 opens the valve seat 9 of the pressure limiting valve 7. Thus, fluid can flow via an obliquely radially routed branch duct 30 through the housing 27 of the pressure limiting valve 7 and the wall of the main control section 23 to a secondary connection 31, which is connected to a pressure medium tank. Hence, on the orifice 21 of the orifice bore 11 on the back side of the piston in the spring space, a pressure drop arises and propagates to the pilot chamber. This results in the valve piston 2 moving in the direction of the fluid inlet 4 and in enabling a flow connection to the fluid outlet 5.

The described combination valve can replace the independent pressure limiting valve, shown in the prior art, to protect the system pressure by the integration of the pressure limiting function into the proportional throttle valve, as a result of which an expensive valve can be completely omitted. In addition, it is possible to achieve a cost reduction by a simplified “drilling” in the control block (eliminating valve installation space and various connecting bores) and to save installation space on site. In particular, for applications in which a pressure limitation, which is variable depending on the operating state of the lifting means, is desired and which is implemented electronically, the valve according to the invention is suitable for implementation of an additional mechanical protection for safety reasons in case of a fault in the electrical control circuit. In the electronic pressure limitation function, the pressure is detected via pressure sensors and evaluated by a control electronics system that, when a pressure is exceeded, electrically actuates the proportional valve and thus the opening cross section is set such that the pressure at the fluid inlet 4 is kept constant according to the setpoint stipulation. This is critical, based on safety-relevant aspects and, in addition, should be mechanically protected for protection of the system components, for which a conventional pressure limiting valve (not shown) would also be necessary here, which can be omitted at this point within the scope of the inventive solution. 

1. A proportional throttle valve comprising a valve piston (2) which is movably guided in the longitudinal direction in a valve housing (3) having a fluid inlet (4) and a fluid outlet (5) and which is pretensioned by an energy accumulator, in particular in the form of a compression spring, against a stroke stop (6) defining the closed position, characterized in that the proportional throttle valve (1) integrates a pressure limiting valve (7), using which the fluid pressure on the back side (8) of the valve piston (2), for purposes of moving away from the stroke stop (6) which takes place against the pretensioning, is influenced when a definable pressure is exceeded at the fluid inlet (4).
 2. The proportional throttle valve according to claim 1, characterized in that the pressure limiting valve (7) is integrated into the valve piston (2).
 3. The proportional throttle valve according to claim 1, characterized in that a fluid pressure at the fluid inlet (4) of the proportional throttle valve (1) acts on a valve seat (9) of the pressure limiting valve (7).
 4. The proportional throttle valve according to claim 3, characterized in that the fluid pressure on the fluid inlet (4) is routed via a radially offset axial bore (10) in the valve piston (2) to the back side (8) of the valve piston (2) via an orifice (21) and a bore (12) running axially in the valve piston (2) and from this draining radial bore (13) to a pilot chamber for pressure balancing of the valve piston (2).
 5. The proportional throttle valve according to claim 4, characterized in that the fluid pressure at the fluid inlet (4) likewise prevails on the valve seat (9) of the pressure limiting valve (7) and, when a definable value is exceeded, opens it, a pressure drop at the orifice (21) being effected and thus a resulting force on the valve piston (2) arising for purposes of displacing the latter for connection of the fluid inlet (4) to the fluid outlet (5).
 6. The proportional throttle valve according to claim 1, characterized in that the pressure limiting valve (7) maintains its function via the valve piston (2) even in the deenergized state of an actuating magnet system (14) for the valve piston (2). 